There are some mobile terminal devices which may be used in a country other than a contracted country. In a case where a mobile terminal device is allowed to be used in a country other than the contracted country, it is possible that a roaming agreement has been concluded between an operator in the contracted country and another operator in the country other than the contracted country. Radio communication systems provided by an operator may include a GSM (Global System for Mobile Communications) (registered trademark) system and a WCDMA (Wideband Code Division Multiple Access) system. Further, an LTE (Long Term Evolution) system may be included.
A mobile station operates on its home public land mobile network (PLMN: public land mobile network) or equivalent home PLMN. The mobile station selects a PLMN. Two types of selection methods, i.e., an automatic mode and a manual mode, are defined as operations for selecting the PLMN. In the automatic mode, a list of PLMNs in priority order is utilized. The highest priority PLMN among available and allowable PLMNs is selected. In the manual mode, the mobile station indicates available PLMNs to a user. Only when the user manually selects, the mobile station attempts to obtain a service in the selected PLMN.
A case is explained where a PLMN is selected in the automatic mode.
FIG. 1 shows an example of processes from the power-on of a mobile station until the location registration is performed.
The power supply of the mobile station is turned on (step S12).
The mobile station performs a cell search (step S14). The mobile station detects available frequency ranges and cells that are to be candidates for a serving cell. The cell search may be referred to as a “band search.”
The mobile station performs PLMN selection (step S16). The mobile station selects a PLMN that is available for the mobile station among the cells that are detected at step S14. For example, a USIM (Universal Subscriber Identity Module) card is attached to the mobile station. The USIM card stores a telephone number for which a contract has been established with an operator; and a priority order to be recorded by the operator, which is for establishing a connection with another operator's PLMN. When a PLMN is to be selected in accordance with the priority order, for PLMNs having the same priority order, the mobile station selects the PLMN randomly from the PLMNs whose electric field strengths are greater than or equal to a predefined value. Further, when there are no PLMNs whose electric field strengths are greater than or equal to the predefined value, the mobile station selects the PLMN in accordance with a descending order of signal levels.
The mobile station performs cell selection (step S18). The mobile station detects candidate cells which are available to the mobile station, based on broadcast information from the PLMN which is selected at step S16.
The mobile station performs location registration (step S20). The mobile station selects a cell to which the location registration is to be performed among the cells detected at step S18. Then the mobile station performs the location registration to the selected cell.
A case is explained where a PLMN is selected in the manual mode.
Irrespective of whether the operation mode is the manual mode or the automatic mode, when the power supply of the mobile station is turned on, or when the mobile station returns from an out-of-coverage state, the PLMN is selected to which the location registration has been performed at a previous time. In the automatic mode, for a case where there are no PLMNs to which the location registration has been performed at the previous time, another PLMN is automatically selected. In the manual mode, after that, it is possible for a user to manually select another PLMN.
In the manual mode, for selecting the PLMN, only the detected PLMNs are displayed in a list, and the user selects one PLMN from the list. It is not possible to select PLMNs that are not detected.